1. Field of the Invention
The present invention relates to plasma processing apparatus and method, and particularly to a plasma processing apparatus and method suitable for making surface treatment of a sample such as a semiconductor device by use of plasma.
2. Description of the Related Art
In the etching process using plasma, the processing gas is ionized to be activated for fast processing, and radio frequency (RF) biasing power is supplied to the processed sample so that the ions in the plasma can be incident perpendicularly to a sample to be processed (or a processed sample), thereby achieving high-precision etching for anisotropic shape and so on.
A plasma processing apparatus for this purpose is disclosed in U.S. Pat. No. 5,891,252, issued to Yokogawa, et al. This apparatus, as described in that document, has an air-core coil provided on the outer periphery of the outside of a vacuum vessel, and a circular conductor plate provided to oppose a wafer stage or substrate electrode within the vacuum vessel. In addition, an UHF band power supply and a first RF power supply are connected to the circular conductor plate, while a second RF power supply is connected to the wafer stage, so that an electric field of UHF band and anther electric field of frequencies different from the UHF band are superimposed and applied to the circular conductor plate. Thus, plasma is generated by use of electron cyclotron resonance due to the mutual action between the electromagnetic waves from the UHF band power supply and the magnetic field from the air-core coil. The superimposed RF voltage from the first RF power supply increases the bias voltage to the circular conductor plate so that the circular conductor plate and the plasma can be reacted to more produce activated species that contribute to the etching, and the second RF power supply connected to the wafer stage controls the energy of ions incident to the sample in the plasma.
In this conventional apparatus, the energy of ions incident to the processed sample is determined by the self-bias potential that is caused by the biasing power fed to the processed sample, and since the rate of the earthed area to the substrate electrode is reduced as the wafer size, or diameter increases, a large amount of electrons from the plasma cannot be supplied to the substrate electrode. Therefore, the Vdc/Vpp ratio becomes small, and the plasma potential increases. Thus, such problems occur as to reduce the efficiency of applying the RF bias, to cause metal contaminant resulting from the sputtering of ions in the plasma to the earth electrode and side wall materials, and to increase particles due to the diffusion of the plasma into the space below the processing chamber.
In addition, since a sinusoidal RF electric field is applied to the wafer stage, (or substrate electrode), the ion energy distribution is fixed under the RF bias of a fixed frequency. Thus, when a processed sample as represented by SAC (Self Aligned Contact) is tried to process with the etching speed maintained constant as the semiconductor device is micro-structured more and more, the selectivity to mask and base material is small, and hence it is difficult to process with high precision.
It is the first object of the invention to provide a plasma processing method and apparatus capable of making high-precision surface treatment with the selectivity to the mask and/or base material kept large enough.
It is the second object of the invention to provide a plasma processing method and apparatus capable of suppressing the plasma potential from being raised, and thereby suppressing the metal contaminant and particles from being increased.
The above objects can be achieved by providing a plasma processing method for processing a sample by plasma while bias voltages to plasma generation and the sample are each being controlled independently, this method having the steps of applying an RF voltage as one of the bias voltages to a substrate electrode, and flattening the voltage waveform of the RF voltage at an arbitrary voltage level.
In the above method, the voltage waveform of the negative voltage side of the RF voltage to the substrate electrode is flattened.
The voltage waveform of the positive voltage side of the RF voltage to the substrate electrode is flattened.
The voltage waveforms of the positive and negative voltage sides of the RF voltage to the substrate electrode are flattened.
The plasma processing method further has the steps of providing an electrode opposite to the substrate electrode, applying RF voltages of the same frequency to both the electrodes, and controlling the phases of the RF voltages.
According to one aspect of the invention in order to achieve the above objects, there is provided a plasma processing apparatus including a processing chamber connected to a vacuum exhauster so that its inside pressure can be reduced by the vacuum exhauster, a gas feed unit for supplying gas into the processing chamber, a substrate electrode provided in the processing chamber and on which a sample can be placed, an RF power supply connected through a matching circuit to the substrate electrode, plasma generating means for producing plasma in the processing chamber, and a voltage waveform control circuit provided within the matching circuit or between the substrate electrode and the matching circuit to flatten the voltage waveform from the RF power supply.
In the above apparatus, the voltage waveform control circuit flattens the negative voltage side of the RF voltage waveform to the substrate electrode at an arbitrary voltage level.
The voltage waveform control circuit flattens the positive voltage side of the RF voltage waveform to the substrate electrode at an arbitrary voltage level.
The voltage waveform control circuit flattens the positive and negative voltage sides of the RF voltage waveform to the substrate electrode at arbitrary voltage levels.
The voltage waveform control circuit includes a semiconductor device and a DC voltage source.
The plasma processing apparatus further includes an electrode opposite to the substrate electrode, and another RF power supply connected to the opposite electrode.
Also, the frequencies of the RF voltages applied to the two electrodes are made equal, and the plasma processing apparatus further includes a phase control for controlling the phases of the RF voltages.
According to another aspect of the invention, there is provided a plasma processing method for processing a sample by plasma while bias voltages to plasma generation and the sample are each being independently controlled, the method having the steps of applying an RF voltage as one of the bias voltages to a substrate electrode, and flattening the positive and negative voltage sides of the voltage waveform of the RF voltage at arbitrary voltage levels.
The above method further has the steps of providing an electrode opposite to the substrate electrode, applying RF voltages of the same frequency to both the electrodes, and controlling the phases of the RF voltages.
The phases of the RF voltages are made to have a difference of 180xc2x0xc2x130xc2x0.
According to another aspect of the invention, there is provided a plasma processing apparatus including a processing chamber connected to a vacuum exhauster so that its inside pressure can be reduced by the vacuum exhauster, a gas feed unit for supplying gas into the processing chamber, a substrate electrode provided in the processing chamber and on which a sample can be placed, an RF power supply connected through a matching circuit to the substrate electrode, plasma generating means for producing plasma in the processing chamber, and a voltage waveform control circuit provided within the matching circuit or between the substrate electrode and the matching circuit to flatten the positive and negative voltage sides of the RF voltage waveform at arbitrary voltage levels.
In the above apparatus, the voltage waveform control circuit has a diode and a DC voltage source.
The apparatus further includes an electrode opposite to the substrate electrode, and another RF power supply connected to the opposite electrode.
Also, in the apparatus, the frequencies of the RF voltages applied to the two electrodes are made equal, and the apparatus further includes a phase control for controlling the phases of the RF voltages.
The phase control can control the phases to have a difference of 180xc2x0xc2x130xc2x0.
According to another aspect of the invention, there is provided a plasma processing method for processing a sample in a processing chamber in which plasma is produced, the method having the steps of applying an RF voltage to a substrate electrode on which the sample is placed, and flattening the voltage waveform of the RF voltage at an arbitrary voltage level.
In the above method, the voltage waveform of at least one of the positive and negative voltages of the RF voltage applied to the substrate electrode is flattened.
According to another aspect of the invention, there is provided a plasma processing apparatus including a processing chamber connected to a vacuum exhauster so that its inside pressure can be reduced by the vacuum exhauster, a gas feed unit for supplying gas into the processing chamber, a substrate electrode provided in the processing chamber and on which a sample can be placed, an RF power supply connected through a matching circuit to the substrate electrode, and a voltage waveform control circuit provided within the matching circuit or between the substrate electrode and the matching circuit to flatten the voltage waveform at an arbitrary voltage level.
In the above apparatus, the voltage waveform control circuit can flatten at least one of the voltage waveforms of the positive and negative voltages of the RF voltage applied to the substrate electrode.
Thus, the energy distribution of ions incident to the sample can be controlled by controlling the RF voltage waveform applied to the substrate electrode, so that the ion energy can contribute chiefly to the etching of the processed sample, but does not contribute to the etching of the mask and base material. Therefore, high-precision surface processing can be carried out with the etching speed not greatly changed and with the selectivity to the mask and base material assured to be large enough.
In addition, by flattening the negative voltage of the RF voltage to the substrate electrode, it is possible to narrow the width of the widely spread ion energy distribution, to obtain the energy distribution in which a large amount of ion energy useful for the processing is included, and hence to improve the efficiency of processing the sample by plasma.
Moreover, by flattening the positive voltage side together with the negative voltage side, it is possible to obtain stabilized plasma potential, and to stabilize the processing of the sample in the plasma. Also, since the influence of the plasma sheath characteristic distribution in the surface of the sample due to the plasma characteristic distribution in the surface is reduced, the charging damage can be suppressed, and thus high-precision etching can be carried out with less damage.
Furthermore, by providing an electrode opposite to the substrate electrode, applying the RF voltages of the same frequency to both the electrodes, and controlling the phase difference between the RF voltages to be 180xc2x0xc2x130xc2x0, it is possible to suppress the potential of the positive voltage side of the RF voltage from increasing, and hence to obtain stabilized plasma potential, thus leading to the stabilization of plasma processing.